Question 299454
Simply take half of 9 to get {{{9/2}}}. Now square {{{9/2}}} to get {{{81/4}}}. Add this to {{{t^2-9t}}} to get {{{t^2-9t+81/4}}}. It turns out that you can factor {{{t^2-9t+81/4}}} to get {{{(t-9/2)^2}}}. 



So {{{t^2-9t+81/4=(t-9/2)^2}}}